1. Field of the Invention
The present invention relates to an optical pickup actuator for which a moving unit performance, due to heat, is not reduced when used as a slim, or miniaturized, optical pickup actuator, and an optical recording and/or reproducing apparatus and method for the same.
2. Description of the Related Art
Generally, optical pickups are used in optical recording and/or reproducing apparatuses to record and/or reproduce information on an optical disc, without contacting the disc, while moving along a radial direction of the optical disc. Optical pickups include an optical pickup actuator for driving an objective lens in tracking and focusing directions of the optical disc to radiate a light spot on a desired track of the optical disc.
In portable devices, such as a notebook computers, an optical recording and/or reproducing apparatus must be made to be slim and lightweight. However, available space for installing an entire recording and/or reproducing system of the portable devices is limited. Thus, an optical pickup actuator used in the portable devices is required to be slim.
In portable devices, an optical pickup includes a mirror for reflecting incident light toward an objective lens. In order to reduce the distance between the objective lens and the reflecting mirror of the optical pickup, to make the optical pickup slim, an asymmetric optical pickup actuator has been proposed with a driving axis of the optical pickup actuator and an optical axis of the objective lens being disposed differently from each other.
FIG. 1 is a perspective view schematically showing one example of a conventional asymmetric optical pickup actuator.
Referring to FIG. 1, the conventional asymmetric optical pickup actuator includes a blade 2, with an objective lens 1 placed on one side thereof, a plurality of wires 6, and a magnetic circuit. One end of each of the plurality of wires 6 is coupled to the blade 2 and the other end is fixed to a holder 3, provided on a base 9, such that all components of a moving unit including the blade 2, can move in a focusing direction F and a tracking direction T with respect to the base 9. The magnetic circuit thereby drives the moving unit in the focusing direction F and the tracking direction T.
The magnetic circuit includes focusing coils 4 and tracking coils 5 which are installed on the blade 2, a pair of magnets 7 that generate an electromagnetic force by interacting with current flowing in the focusing coils 4 and the tracking coils 5, to drive the moving unit, and a yoke 8.
When current is applied to the focusing coils 4 and the tracking coils 5, an electromagnetic force generated, due to interaction between the current flowing in the focusing coils 4 and the tracking coils 5 and the magnetic flux of the magnets 7 being applied to the focusing coils 4 and the tracking coils 5, thereby drives the moving unit in the focusing direction F and the tracking direction T. The objective lens 1 placed on the blade 2, accordingly, moves in the focusing direction F and the tracking direction T.
However, in the conventional asymmetric optical pickup actuator, since the coil, particularly, the focusing coils 4, is directly in contact with the blade 2, in which the objective lens 1 is mounted, heat generated by applying current to the coils 4 and 5 is directly transferred to the blade 2 and the objective lens 1, thereby reducing the rigidity of the blade 2. Thus, the performance of a conventional design of the asymmetric optical pickup actuator is deteriorated, resulting in the control performance being changed and the objective lens 1 being damaged.
Particularly, it is relatively difficult to disperse heat from a slim optical recording and/or reproducing apparatus because the corresponding actuator is placed inside an optical pickup and because the size of the resultant optical pickup is smaller than other asymmetrical optical pickup designs for non-portable devices. Since the coils 4 and 5 directly act as heat sources for the moving unit when installed in the blade 2, the rigidity of the blade 2 is reduced at least because of the temperature problem inside portable devices, e.g., a notebook computer. Thus, the performance of a conventional design of the optical pickup actuator deteriorates so much so as to change tracking and focusing control performance.
For example, according to this conventional optical pickup actuator structure, a second resonance frequency exists around 20 kHz, before applying current. However, the second resonance frequency moves to around 10 kHz, due to reduction in the rigidity of the blade 2, after current is applied and heat is generated.
Changes in control performance, due to heat as described above, accounts for a large portion of defects in products.
Further, according to this conventional optical pickup actuator structure, where the coils 4 and 5 are installed on the moving unit, a plurality of components, for example, a printed circuit board (PCB) 10 and the wires 6 for electrical connection, must be installed on the blade 2 to apply current to the coils 4 and 5, in addition to the required additional soldering process.
As a height of the slim optical pickup actuator may be about 4-5 mm, soldering must be performed within a range of a thickness of 1 mm or less.
Thus, the soldering process must be performed manually, thereby limiting the mass-productivity of production of the optical pickup actuator. Further, the defect rate of the actuator increases, including large deviations between optical pickup actuator assemblies as a result at least due to the manual soldering process.
Further, six wires are required for driving an optical pickup actuator for triaxial movement in a focusing direction, a tracking direction, and a radial tilt direction. However, the optical pickup actuator is restricted in space, making it difficult to install the required plurality of wires. As the number of wires increases, the process for installing the wires becomes more difficult, thereby increasing the defect rate of the actuator.
In addition, in the conventional optical pickup actuator, since only about ¼ of a total length of the focusing coils 4 is used, in effect, to control the actuator. The unnecessary portion of the focusing coils 4 also prevents the actuator from being reduced in size and increases the asymmetry of the actuator.